Compositions based upon polyamine crosslinkers and compounds containing amine-reactive functionalities ("binders") are well-known in the literature. As examples of such amine-reactive functionalities in combination with polyamine crosslinkers may be mentioned:
(i) activated unsaturated groups such as (meth)acryloyl groups and other groups derived from maleic acid and anhydride, fumaric acid, and itaconic acid and anhydride; PA1 (ii) activated methylene groups such as acetoacetate and malonate groups; PA1 (iii) epoxy groups; PA1 (iv) isocyanate groups; PA1 (v) aromatic activated aldehyde groups; PA1 (vi) cyclic carbonate groups and PA1 (vii) acid, anhydride, and ester groups, including oxalate esters. PA1 R.sub.1 is hydrogen or a substituted or unsubstituted hydrocarbon group, optionally containing a functional group; PA1 at least one of R.sub.2 and R.sub.3 is a substituted or unsubstituted alkylene group; PA1 at most one of R.sub.2 or R.sub.3 is a group of the formula (II) or (III) ##STR3## wherein R.sub.4 is a substituted or unsubstituted alkylene group, and the N atom is attached to both B and the other of R.sub.2 or R.sub.3, PA1 R.sub.5 is a substituted or unsubstituted alkylene group and R.sub.6 is hydrogen or a substituted or unsubstituted alkyl group, while either R.sub.5 or R.sub.6 is attached to B; PA1 n.gtoreq.2; and PA1 the ring defined by R.sub.3, R.sub.2, and N=C in formula (I) consists of 4-12 atoms. PA1 (I) Reacting 1) a compound comprising at least one internally blocked amino group and one secondary amino group which is part of the ring and 2) a substantially stoichiometric amount of a monomer or an oligomer comprising at least two amine-reactive groups (i.e., the monomeric or oligomeric backbone); PA1 (II) Reacting, under moisture-free conditions, 1) a compound comprising at least one internally blocked amino group and 2) a substantially stoichiometric amount of a monomer or an oligomer comprising at least one, preferably at least two, Michael acceptor moieties; PA1 (III) Reacting 1) a compound comprising at least one internally blocked amino group and one nucleophilic moiety pendant from the ring and 2) a substantially stoichiometric amount of a monomer or an oligomer comprising at least two nucleophilic-reactive (or electrophilic) moieties.
For examples of publications describing the above groups in more detail reference is made to WO 94/15974.
In general, the amino groups of the traditional polyamine crosslinkers are quite reactive with the above-mentioned functionalities under ambient or low (less than 120.degree. C.) temperature conditions. This can result in a too short potlife and consequent application problems.
In many of the above systems, therefore, the highly reactive amino groups of the polyamine crosslinkers are blocked in order to allow the formulation of systems with an acceptable potlife. For primary amino groups, the common blocking agents are ketones and aldehydes, resulting in, respectively, ketimines and aldimines. The reaction sequence is as follows: ##STR1##
The resulting imine group is stable under anhydrous conditions, but relatively unstable even in the presence of atmospheric humidity. This property has been utilised quite successfully in low and ambient temperature cure applications. The use of these kinds of ketimines and aldimines, however, has certain disadvantages.
For example, the deblocking of the primary amino group results in the liberation of a volatile ketone or aldehyde. This liberated component not only adds to the overall VOC (Volatile Organic Content) of the system, but can also have detrimental consequences to the appearance characteristics of the resulting crosslinked products (e.g., clouding in clearcoat applications).